Radio apparatus



Aug. 7,1934. c. J. HIRSCH 1,968,889

RADIO APPARATUS Filed Aug. 6; 1930 DETECTOR INVENTOR CHARLES J. HIRSCHATTORN EY Patented Aug. 7, 1934 Charles J. Hirsch, New to Thomas A. EdisOrange, N. J., a corpo Application August 26,

5 Claims.

This invention relates to radio apparatus and more particularly to radioreceiving apparatus intended to cover relatively wide ranges offrequency.

It is an object of this invention to provide apparatus of the classdescribed which will operate to select signals within a predeterminedband of frequencies and in which the particular band of frequencies tobe received may be shifted as desired. a l It is a further object ofthis invention to provide apparatus of the class described which doesnot require a change of coils or the like when it is desired to changethe band to be covered.

Itis a further object of this invention to provide radio receivingapparatus which is particurlarly adapted to receive stations operatingwith,- in the broadcast spectrum and which may be adju'sted to receivesignals of either higher or lower frequencies.

It is a further object of this invention to provide apparatus of theclass described in which the apparatus may be converted from a broadcastreceiver to receive frequencies higher or lower than the broadcastfrequencies without the insertion or removal of special coils or thelike.

Still other objects and advantages of my invention will be apparent fromthe specification.

The features of novelty which I believe to be characteristic of myinvention are set forth with particularity in the appended claims. Myinvention itself, however, both as to its fundamental principles and asto its particular embodiments, will best be understood by reference tothe specification and accompanyingdrawing, in which Figs. 1 and 2illustrate the type of circuit utilized to provide a shift in thereception band,

Fig. 3 shows one form of receiving apparatus in accordance with myinvention,

I Fig. 4 shows a modified form of receiving apparatus in accordance withmy invention, and

Fig. 5 shows still another form of receiving apparatus in accordancewith my invention.

In the various figures, like reference numerals indicate like parts.

At the present time the radio broadcasting frequency band coversapproximately the range between 550 to 1500 kilocycles and all broadcastreceiving apparatus is particularly designed so as to cover this band.However, matters of interest to the public are also transmitted on otherfrequencies, for example at very much higher frequencies, as in the.so-called short waves.

I am awarethat it has been proposed in the past to utilizebroadcastreceiving apparatus for receiving either higher or lowerfrequencies outside of -the broadcast range by removing the transformersor coils and substituting different masses RADIO APPARATUS Rochelle, N.Y., assignor on, Incorporated, West ration of New Jersey 1930, SerialNo. 477,853 (Cl. 178-44) transformers or coils, particularly designedtocover other ranges. This procedure is open to many objections, amongwhich may be mentioned the necessity of having on hand additional setsof transformers or coils which may be substituted for those in use, thedifficulty of arranging the apparatus so that it is mechanically stablewhile at the same time the transformers or coils are accessible so as tobe easily removed and replaced, the difliculty of maintainingqelectricalefficiency-particularly dueto the tendency of the contactson'the coilsor transformers and assoe ciated apparatus to corrode or oxidize withresultant decrease inefficiency of the receiver, and the additional costinvolved in providing the extra coils or the like, and in arranging theapparatus to provide for the substitution of coils.

In accordance with one aspect of my invention, I ,eliminate thenecessity for changing transformers or coils when it is desired tochange the band of frequencies to be received, by utilizing coupledcircuits and controlling the coupling between the circuits in such amanner as to shift the band to be received. The coupling between thecircuits may be constituted by capacity, selfinductance, or mutualinductance.

Referring now particularly to Fig. 1, it will be seen that inductanceL1, capacity C1 and Cm con stitute one tuned circuit. Inductance L2,capacity C2 and capacity Cm constitute a second tuned circuit. Thesecircuits are coupled through the capacity Cm which 'is'common to the two.cir cuits. It is known that under certain conditions such coupledcircuits give rise to, peaks occurring at different frequencies.

If the two circuits have their. constants so chosen as to be separatelyresonant to the same frequency, which is represented as am, for example,if L1=L2 and C1=Cz, neglecting the resistance of the circuits, therewill be two peaks or frequencies of maximum response, one of which If L1and 'C1 are already fixed by the require ment of one frequency band, asuitable value of Cm can be chosen to cover another band A suitablevalue of C1 can be chosen if L1 and Cm are fixed.

The circuit will also respond to a frequency determined by Equation (2)which can be rewritten as (obtained by the substitution in Equation (2)of the values of wt and K given by Equation (3) and (4).

If we are interested only in w1 and vary the tuning by varying Cm itwill be seen that wz is independent of the value of Cm and can beremoved by a simple filter, since it does not change. with variation inCm.

This happens because the values of wo and K are both affectedsimultaneously by changes in the value of Cm, in such a manner that thevalue of 0:2 is left unchanged by variations in the value of Cm.

Referring now more particularly to the circuit shown in Fig. 2, which isgenerally similar to the circuit of Fig. 1, except that the coupling isnow obtained by a common self-inductance, Lm instead of capacity Cm,this circuit is responsive to two frequencies as before, but thefrequencies are now given by the following:

Substituting these values in Equations (7) and (8) I obtain Thus thecircuit may be selective to a frequency determnied by L and C1 alone,and in operation the band to be received may be controlled by varyingthe value of the capacity Cm or the inductance Lm, after which stationswithin the band may be selected by varying the capacities C1 and C2.

The formulae (7) and (8) developed in connection with Fig. 2 above applyalso where the coupling between the circuits is of the type shown inFig. 3 (i. e., by mutual inductance instead of a common selfinductance),in which case it will be found that Where, for example, L1 is theself-inductance of coil 4 and C1 the capacity of condenser 3 and valueof K may be altered without affecting the value of. am, both we and (04will vary with changing values of K.

In general, it may be stated that'whatever the nature of the couplingbetween the circuits, as the coupling is made less, 601 and wz, the twomaximum response frequencies of the system approach each other andapproach the resonant frequency of the individual tuned circuits, andconversely as the coupling is tightened, the greater the differencebetween them.

From the foregoing mathematics we may tabulate the results forcomparative purposes. In making this tabulation it should be borne inmind that in the case of the circuit shown in Fig. 3 where the couplingis by mutual inductance and not by a common self-inductance, thetabulation may be simplified by the use of an additional formula, whichis where L1 isthe total inductance in the individual circuit and is, ofcourse, made up of the two components L0, the self inductance of thecircuit, considered separately, plus Lm, which is the mutual inductanceor the inductance common to the two circuits by reason of the flux whichinterlinks the primary and secondary coils.

In the following table the first column of formula represents the valueof wz for the three circuits shown respectively in Figs. 1, 2 and 3; thecenter column the formulae for we for the same three cases, and thethird column the formulae for w1 for the same three cases. The figuresin parenthesis refer to the formulae already derived.

The formulae in the above table, in some cases, are in slightlydifferent form from those indicated by the reference numerals, butmathematically they are identical.

From this it will be seen that in the case of the circuit shown in Fig.1, when the coupling capacity is varied wz remains constant, weapproaches infinity as a limit and w1 also approaches infinity as alimit but w1 is always greater than 0.10.

For the circuit shown in Fig. 2, as the coupling between the circuits isincreased, wl remains constant, wo approaches zero as a limit and wzapproaches zero as a limit, but wz is always less than n01.

For the circuit of Fig. 3, it will be seen that as the coupling betweenthe circuits is tightened (.00 remains unchanged, wz decreases,approaching 0.7 we as a limit, and w1 increases approaching infinity asa limit. It will be understood that the limiting case is represented bythe condition where the coefficient of coupling is equal to one.

It should also be remembered that of these three frequencies wo, w]. andwz, only 0)]. and wz are actual response or hearing frequencies. wo fromits definition, is a hearing frequency only when the coupling isextremely loose appreaching zero, in which case as a practicalmatter aand (a, which are the hearing frequencies lie very close together. Inpractice this is the condition which obtains when the receiver is tunedto a broadcast frequency, in which case an and (02 might differ by say 5kilocycles and mo lying between the'm would also be heard.

Referring now more particularly to Fig. 3 in which I have showndiagrammatically one form of radio receiver embodying this invention,there is provided an antenna 1 and condenser 2. The first resonantcircuit comprises condenser 3, and coil 4, and the first resonantcircuit is coupled to a second resonant circuit comprising condenserSand coil 5 through the medium of coils 4 and 5, the coupling betweenwhich is made variable in any suitable way. The lower ends of the coils4 and 5 and the corresponding plates of the condensers 3 and 6 may beconnected together and to ground as shown. The output of the secondcircuit may be amplified to the amount desired by an amplifier 7 andpassed through any suitable type of filter, the output of which may bedetected by any suitable-detector 9 and supplied to any suitableindicating device such as receivers 10. r J

If the constants of condensers 3 and 6 and coils 4 and 5 are the sameand are so chosen that the circuits separately are tuned to 550kilocycles,

with the condensers set for maximum capacity, the combination comprisingcondenser 3 and coil 4 and condenser 6 and coil 5 coupled through themutual inductance of coils 4 and 5 will have peaks occurring at twofrequencies given by and a difference appears between the circuits shownin Figs. 1 and 2, where the coupling is by common capacity and commonself-inductance respectively, and the circuitshown in Fig. 3, where thecoupling is by mutual inductance. It should be noted that in the case ofthe circuits in Figs. 1 and 2 variation of the common condenserCm or ofthe common inductance Lm will cause a variation of the frequency we towhich each of the circuits when considered separately is tuned, whereasin the case of Fig. 3 the coupling being mutual inductance only may bevaried without changing wo. Variation of the mutual inductance onlywithout changing the self-inductance of] either of the coils coupledthrough a mutual inductance, as is well known, may be obtained in anumber of known ways, such for example, as varying the distance betweenthe coupled coils or varying the relative direction of their axes as byrotating one or the other. If it is desired to receive stations in theneighborhood of 2750 kilocycles, signals in the neighborhood of 393kilocycles, if present, will be undesired and may beliremoved bythefilter 8 constructed in any known way to remove frequencies in thisneighborhood. This filter may advantageously be a sol-called high-passtype suppressing fre-'- quencies below the lowest frequency desired tobe received, which in this instance would be 550 kilocycles. Of courseit will be understood that if there are no stations transmitting in theneighborhood of this undesired frequency the filter may be omitted andit will be understood that by proper selection of the constants thesecond peak may be made to fall at any desired point, within limits.

If the coupling be made still tighter, for examp1e, 0.99 the upper peakwill occur at a still higher frequency, in this case 5500 kilocycles.Thus it will be seen that without changing the coils or condensers, theupper peak can be shifted from 550 kilocycles to 5500 kilocycles whilestill keeping each of the circuits respectively comprising condenser 3and coil 4, and condenser 6 and coil 5, when considered separately,tuned to 550 kilocycles, that is with the variable condensers 3 and 6set to their maximum value. If the variable condensers are set totheir'minimum value so that the resonant circuits would be separatelytuned to 1500 kilocycles, then with a coupling of 0.99 the upperfrequency will become 15,000 kilocycles. Tuning may be accomplishedeither by variation of the coupling coefficient to the proper value, asby varying'the coupling between coils 4 and 5 without any other changeor it may be accomplished by changing the coefficient of coupling insteps to give an approximate tuning and by variation of the tuningcondensers 3 and;-6 to give the final selection of the desiredfrequency.

In cases where it is desired to obtain very high coupling between thetwo circuits it may be difficult to obtain suflici'ently close couplingmerely by bringing coils 4 and 5 together, and in this case additionalinductances 11 and 12 may be inserted as shown in Fig. 4 and coils 4 and5 replaced by inductance 13. The inductance 13 may be the usual tuninginductance of a broadcast receiver and may have a value of 200. mhs. Forexample, it may be either coil 4 or (3011 5 alone. Then if theinductances 11 and 12 are made to have a value of 2 rubs. thecoefficient of coupling will be Referring now more particularly to Fig.5, I have shown a radio receiver embodying alternate steps of selectionand amplification repeatedly. In this instance the first pair ofselecting circuits comprises inductances 21- and 25, tuning condensers22 and 24 andcoupling condensers 23, coil 21 being coupled to coil 20 incircuit with antenna 1. The output of the first pair of circuits may beamplified by any suitable amplifier such, for example, as vacuum tubehaving an anode 28, cathode 26 and control electrode 27, anodepotentialbeing supplied by a suitable source 29. Since the construction andoperation of amplifiers is well known in the art and forms, per se, nopart of the present invention, the same is not described in detail.

The second pair of selecting circuits is made up by inductances 31 and35, tuning condensers32 and 34 and coupling condenser 33. is coupled tocoil 30 connected to the anode 28 of the previous amplifier. The secondpair of selecting circuits is similar to the first pair alreadydescribed and is therefore not described in detail. Similarly the outputof the second pair The coil 31 i of selecting circuits may be amplifiedby a second amplifier comprising anode 38, cathode 36 and controlelectrode 37, the anode being energized from a suitable source orpotential 39.

The output of the second amplifier may be still further selected andamplified if desired, or amplified without further selection or furtherselected without further amplification. In the arrangement shown I haveindicated a filter following the output of the second amplifier, saidfilter comprising condensers 41 and 43 and inductances 4Q, 42 and 44,having constants so chosen as to bypass any undesired frequencies andmore particularh the low frequency peak arising from the action of thecoupled circuits as already described. The amplified and selectedcurrents may then be detected in any suitable manner as, for example, bya vacuum tube detector comprising an anode 49, cathode 47 andcontrolelectrode 48 to which is connected grid condensers 45 and gridleak 46. A suitable source of potential 50 is provided for energizingthe anode 49 and any suitable indicator such as receivers 10 may beconnected thereto, it being understood of course that the signals may befurther amplified after being detected before being supplied to theindicator.

The variable tuning condensers 22, 24, 32 and 34 may be all connectedtogether and to a single operating means if desired, and similarly thevariable coupling condensers 23 and 33 may be connected together and toa single operating means. If it is desired to use the apparatus as abroadcast receiver, the coupling condensers 23 and 33 will be set tosuch a value that the coupling between the coupled resonant circuits isof the order of 1%. The desired broadcast signal may then be tuned inthe usual way. If a frequency above the broadcast frequency is desired,condensers 23 and 33 are then adjusted to give tighter coupling, asalready described. Selection of the signal may then be made, either byvariation of coupling or by variation of the tuning condensers.

While I have shown and described my invention with particularapplication to radio frequency currents, it will be understood that itis not limited thereto, but is capable of use in many other arrangementswherein it is desired to select or separate currents of one frequency orband of frequencies from those of another and that modifications andchanges may be made without departing from the spirit and scope of myinvention, as will be understood by those skilled in the art.

I claim:

1. Radio receiving apparatus comprising, in combination, asignalcollecting circuit, a selecting circuit, and a circuit to be suppliedwith selected signals, said circuits being arranged in cascade relation,and said selecting circuit comprising a pair of resonant circuits, eachseparately tunable from 550 to 1500 kilocycles and having a commoncoupling reactance variable with respect to the reactances of saidresonant circuits over such a range that said selecting circuit may becaused to respond to two frequencies simultaneously one of which is morethan 1500 kilocycles and the other of which is less than 550 kilocycles.

2. Radio receiving apparatus comprising, in combination, a signalcollecting circuit, a selecting circuit, a circuit to be supplied withselected signals, and a circuit for suppressing signals having afrequency below a predetermined value, said circuits being arranged incascade relation, and said selecting circuit comprising a pair ofresonant circuits, each separately tunable over only a portion of thedesired frequency spectrum, and having a common coupling reactance ofsuch value relative to the reactances of said resonant circuits that thesaid selecting circuit may be caused to respond to two frequencies, oneof which lies below the frequency of said suppressing circuit.

3. Radio apparatus for receiving signals of a desired frequency lyingwithin an extremely wide band of frequencies, comprising, incombination, a signal collector, a signal selecting circuit, and acircuit to be supplied with selected signals, said signal selectingcircuit comprising a pair of similar resonant circuits, each tunablealone over the same predetermined frequency band considerably smallerthan the total band to be covered by said receiving apparatus, saidcircuits being coupled together by a common variable reactance, therange of variability of said reactance being so chosen with respect tothe constants of said circuits that the coupling between them may bevaried from extremely loose to extremely tight, whereby the two responsefrequencies of said coupled circuits may be selectively caused to occureither substantially together and inseparable, or widely displaced andeasily separable, and means for suppressing one of said responsefrequencies when widely displaced from the other.

4. Radio apparatus for receiving signals of a desired frequency lyingwithin an extremely wide band of frequencies, comprising, incombination,

a signal collector, a signal selecting circuit, a circuit to be suppliedwith selected signals, and a circuit for suppressing signals lying onone side of a predetermined frequency, said signal selecting circuitcomprising a pair of similar resonant circuits, each tunable alone overthe same frequency band, which band is smaller than the total band offrequencies from which reception is desired, said circuits being coupledtogether by a common variable reactance, the range of variability ofsaid reactance being so chosen with respect to the constants of saidresonant circuits that the coupling between them may be varied fromextremely loose to extremely tight, whereby the two response frequenciesof said coupled circuits may be selectively caused to occur eithersubstantially together and substantially inseparable, or widelydisplaced and easily separable, with one of them falling within therange which is suppressed by said suppressing circuit.

5. Radio apparatus for receiving signals of a desired frequency lyingwithin an extremely wide band of frequencies, comprising, incombination, a signal collector, a signal selecting circuit, a circuitfor suppressing signals of less than a predetermined frequency, saidsignal selecting circuit comprising a pair of similar resonant circuits,each tunable alone over a band of frequencies substantially narrowerthan the extremely wide band to be covered by said radio apparatus, saidcircuits being coupled together by a common reactance and means forvarying the coupling between said circuits from extremely loose toextremely tight, whereby the two response frequencies of said couplingsystem may be selectively caused to occur substantially together,.

whereby they are substantially inseparable, or widely spaced and readilyseparable, with the lower of them falling below the range of frequenciessuppressible by said suppressing circuit.

CHARLES J. HIRSCH.

Certificate of Correction Patent No. 1,968,889. August 7, 1934. CHARLESJ. HIRSGH It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows: Page 1, line 110, Equation 3, for "L read L page 2, line 9,Equation 6, for L read L line 11, for Equation read Equations; and line46, Equation 11, for (7 read 0 and that the said Letters Patent shouldbe read With these corrections therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 9th day of October, A. D. 1934.

[SEAL] LESLIE FRAZER,

Acting Commissioner of Patents.

